Re: [PATCH 5/7] scsi: devinfo: replace strncpy and manual pad

[Kees Cook <keescook@chromium.org>]

On Fri, Feb 23, 2024 at 10:23:10PM +0000, Justin Stitt wrote:
> Depending on the state of @compatible, we are going to do different
> things with our @to buffer.
> 
> When @compatible is true we want a NUL-term'd and NUL-padded destination
> buffer. Conversely, if @compatible is false we just want a space-padded
> destination buffer (no NUL-term required).
> 
> As per:
> /**
>  * scsi_dev_info_list_add_keyed - add one dev_info list entry.
>  * @compatible: if true, null terminate short strings.  Otherwise space pad.
> ...
> 
> Note that we can't easily use `strtomem_pad` here as the size of the @to
> buffer is unknown to the compiler due to indirection layers.
> 
> Now, the intent of the code is more clear (I probably didn't even need
> to add a comment -- that's how clear it is).
> 
> Signed-off-by: Justin Stitt <justinstitt@google.com>
> ---
>  drivers/scsi/scsi_devinfo.c | 18 ++++++++++--------
>  1 file changed, 10 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/scsi/scsi_devinfo.c b/drivers/scsi/scsi_devinfo.c
> index 3fcaf10a9dfe..2d3dbce25629 100644
> --- a/drivers/scsi/scsi_devinfo.c
> +++ b/drivers/scsi/scsi_devinfo.c
> @@ -293,14 +293,16 @@ static void scsi_strcpy_devinfo(char *name, char *to, size_t to_length,
>  	size_t from_length;
>  
>  	from_length = strlen(from);
> -	/* This zero-pads the destination */
> -	strncpy(to, from, to_length);

A rare case of the padding intent being expressed! :)

> -	if (from_length < to_length && !compatible) {
> -		/*
> -		 * space pad the string if it is short.
> -		 */
> -		memset(&to[from_length], ' ', to_length - from_length);
> -	}
> +
> +	/*
> +	 * null pad and null terminate if compatible
> +	 * otherwise space pad
> +	 */
> +	if (compatible)
> +		strscpy_pad(to, from, to_length);
> +	else
> +		memcpy_and_pad(to, to_length, from, from_length, ' ');

Yeah, this is much nicer to read.

Reviewed-by: Kees Cook <keescook@chromium.org>

(Some day I want to rename "memcpy_and_pad" ... the "and" seems
verbose...)

-- 
Kees Cook